1. Field of the Invention
The present invention generally relates to optical communication systems, and more particularly, to optical multi-wavelength cross-connect networks for wavelength division multiplex (WDM) optical communications.
2. Statement of the Problem
WDM optical communications systems that can carry information at rates up to terabits per second are becoming the next wave in optical communications development. In current WDM systems, information is optically coded within each of the WDM channels and the network is linked using a point-to-point architecture. Signal routing and switching are performed electronically (i.e., optical information is translated back to electronic format and then processed at each network node). As data rates increase, these opto-electronic and electro-optic conversions are becoming the bottleneck for the network. To improve the efficiency and reduce to cost of networks, routing and switching performed in the optical domain are preferred.
Thus, national and international researches for all-optical networks have become the current focus in the fiber optics industry. A recent technical journal, "Multi-Wavelength Optical Technology and Networks," Journal of Lightwave Technology (vol. 14, no. 6, 1996), has gathered about 40 papers reviewing the current status of all-optical networks. Three basic WDM cross-connect networks were listed (shown herein as prior art in FIG. 1) as the basic building blocks for WDM networks. Recently, a national Optical Multi-Wavelength Optical Networking (MONET) Consortium has been formed to study all-optical networks. In its recent demonstration, three all-optical network test beds have been constructed: a WDM long distance test bed; a WDM cross-connect test bed; and a local-exchange test bed (R. C. Alferness, el. al., "MONET: New Jersey demonstration network results," Optical Fiber Conference 1997, Paper WI1, and "All Optical Test Beds Prove National Networking," Lightwave (April 1997)). Wavelength cross-connect networks using array waveguide gratings (AWG) together with opto-mechanical space switches and LiNbO3-based cross-connect switches have been used in such networks. International efforts, such as the ACTS (Advanced Communications Technologies and Services) program launched by the European Commission projects, are specifically addressing the problems of trans-European optical transport networks using WDM (M. Berger et al., "Pan-European Optical Networking using Wavelength Division Multiplexing," IEEE Comm. Mag. p. 82, (April 1997)). A similar architecture to the MONET project is proposed, except another approach using the wavelength conversion technique is also planned in this European effort.
3. Solution to the Problem
The present invention uses two arrays of unique 1.times.N wavelength switches to form the wavelength cross-connect network. Because the wavelength filtering and optical switching are accomplished within the same device, the switching elements needed to perform the wavelength cross-connect are reduced and optimized. Furthermore, because the wavelength switch has a built-in complementary spectra characteristic, where a wavelength-slicing concept is used, wavelength collision can be avoided.